irqchip/loongarch-avec: Return IRQ_SET_MASK_OK_DONE when keep affinity

Interrupt redirection support requires a new redirect domain, which will
appear as a child domain of avecintc domain. For each interrupt source,
avecintc domain only provides the CPU/interrupt vectors, while redirect
domain provides other operations to synchronize the interrupt affinity
information among multiple cores.

When modifying the affinity of an interrupt associated with the redirect
domain, if the avecintc domain detects that the actual interrupt affinity
hasn't been changed, then the redirect domain doesn't need to perform any
operations.

To achieve the above purpose, in avecintc_set_affinity() when the current
affinity remains valid, then return value is set to IRQ_SET_MASK_OK_DONE.

This doesn't introduce any compatibility issues, even if the new return
value causing msi_domain_set_affinity() to no longer perform the call to
irq_chip_write_msi_msg():

  1) When both avecintc and redirect exist in the system, the msg_address
     and msg_data no longer change after the allocation phase, so it does
     not actually require updating the MSI message info.

  2) When only avecintc exists in the system, the irq_domain_activate_irq()
     interface will be responsible for the initial configuration of the MSI
     message info, which is unconditional. After that, if unnecessary,
     there is no modification to the MSI message info.

Signed-off-by: Tianyang Zhang <zhangtianyang@loongson.cn>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Acked-by: Huacai Chen <chenhuacai@loongson.cn>
Link: https://patch.msgid.link/20260513012839.2856463-4-zhangtianyang@loongson.cn

drivers/irqchip/irq-loongarch-avec.c

@@ -101,7 +101,7 @@ static int avecintc_set_affinity(struct irq_data *data, const struct cpumask *de
 			return -EBUSY;
 
 		if (cpu_online(adata->cpu) && cpumask_test_cpu(adata->cpu, dest))
-			return 0;
+			return IRQ_SET_MASK_OK_DONE;
 
 		cpumask_and(&intersect_mask, dest, cpu_online_mask);